Marker monitoring of oil and gas wells after acid treatments

ABSTRACT

The present disclosure relates to a technique for monitoring the status of an acid-treated oil well by using quantum dot (QD)-based markers. Each of the QD-based markers is a microsphere that is made of hydrophilic or oleophilic materials depending on whether it is intended for water or oil inflow analysis. The hydrophilic microspheres are flushed out with water, while the oleophilic microspheres are flushed out with oil. Each of the microspheres may be filled with the same or different set of QDs. The microspheres are embedded into a porous material which is then placed inside a rigid housing. The housing is provided with a plurality of holes each having a size that is bigger than that of the microspheres. Moreover, the materials of the housing and the microspheres and the porous material are selected such that they are resistant to an acid to be pumped into the oil well.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application relates to U.S. Provisional Patent Ser. No. 63/085,806 filed Sep. 30, 2020, all of which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present disclosure relates generally to the field of production logging. In particular, the present disclosure relates to a production logging apparatus and method which involve monitoring the status of oil wells by using quantum dot (QD)-based markers.

BACKGROUND

The marker (or tracer) technology is one of the most useful tools for oil reservoir characterization. By using this technology, it is possible to obtain relevant data from an oil reservoir, such as a remaining oil accumulation, an oil and/or water inflow profile from the oil well, reservoir heterogeneities, a residual oil saturation quantity, oil and/or water flow channel identification, etc. In general, such a marker is an inert substance that follows a fluid path, traveling along with the fluid present in the oil reservoir without any undesirable reaction. The marker technology usually involves the following two steps: injecting multiple markers into an oil well, and controlling their recovery over time from the oil well for their subsequent quantification and analysis. Although many marker studies have been documented for the oil reservoir characterization, the available information and methodologies related to the design, implementation, and interpretation of marker tests are limited or hidden for confidentiality reasons.

Among the existing marker technologies, the one relying on QD-based markers is of particular interest. This is because the QD-based markers are highly accurate indicators of oil and water inflows. More specifically, this technology involves placing the QD-based markers in a wellbore or in an oil formation by either using a marked polymer-coated proppant injected during multi-stage fracturing or embedding the QD-based markers in special downhole cassettes installed in the lower completion of the wellbore. When reacted with a formation fluid, the QD-based markers are flushed out with water and oil. As a result, the water and oil phases of the formation fluid are automatically provided with their own inflow indicators. The oil and water inflows are then analyzed based on the flushed-out QD-based markers. The advantages of such a marker technology are as follows: it does not require well shut-in or downhole operations during the QD-based tests, as well as it allows obtaining an unlimited amount of analytical data for a long period of time.

However, the above-described QD-based marker technology cannot be applied in acid-treated oil wells. This is, for example, caused by the fact that proppant is an acid-soluble material. Moreover, the existing designs of the downhole cassettes are also not resistant to the conventional acids (e.g., hydrochloric acid) used when performing the acid treatment of the oil wells and/or during multistage acid fracturing.

SUMMARY

This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify key features of the present disclosure, nor is it intended to be used to limit the scope of the present disclosure.

It is an objective of the present disclosure to provide a technical solution that allows the status of acid-treated oil wells to be monitored by using QD-based markers.

The objective above is achieved by the features of the independent claims in the appended claims. Further embodiments and examples are apparent from the dependent claims, the detailed description, and the accompanying drawings.

According to a first aspect, a production logging apparatus attachable to a downhole pipeline is provided. The apparatus comprises a housing made of a housing material. The housing is provided with a plurality of holes each having a hole size. The apparatus further comprises a porous material provided in the housing, as well as a first set of microspheres and a second set of microspheres which are both embedded into the porous material. Each microsphere of the first set of microspheres is made of a hydrophilic material and filled with a first type of QDs. Each microsphere of the second set of microspheres is made of an oleophilic material and filled with a second type of QDs. Each microsphere in each of the first set of microspheres and the second set of microspheres has a microsphere size that is less than the hole size. Moreover, each of the housing material, the porous material, the hydrophilic material, and the oleophilic material is resistant to an acid to be pumped into the oil well. By using the production logging apparatus thus configured, it is possible to monitor the status of oil wells (e.g., oil and water inflows) when or upon performing acid treatment and/or multistage acid fracturing in the oil wells.

In one embodiment of the first aspect, the first type of QDs is identical to the second type of QDs. The same first and second types of QDs may be used when it is sufficient to know a general oil and water inflow profile from the oil well. By using the same first and second types of QDs, it is also possible to reduce the overall manufacturing cost of the production logging apparatus.

In another embodiment of the first aspect, the first type of QDs has a first illumination spectrum and the second type of QDs has a second illumination spectrum that is different from the first illumination spectrum. Due to the different illumination spectra, it is possible to use the first and second types of QDs as identifiers for the first and second sets of microspheres, respectively, thereby making it easier and faster to distinguish between the oil and water inflow profiles from the oil well.

In one embodiment of the first aspect, the microsphere size is selected based on an attachment point of the apparatus to the downhole pipeline. By so doing, it is possible to produce the microspheres that are suitable, for example, for use inside or outside the downhole pipeline. This in turn affects the efficiency of flushing out the microspheres with water and oil and, consequently, the efficiency of the well-status monitoring itself.

In one embodiment of the first aspect, the microsphere size ranges from about 0.2 to 10 microns. This wide range of microsphere sizes may increase flexibility in the selection of the attachment point of the apparatus to the downhole pipeline.

In one embodiment of the first aspect, the porous material comprises a polymer or a sponge-like material. Such a porous material may accommodate a large number of microspheres, as well as allow a fluid (i.e., oil and/or water) to freely flow through itself, thereby facilitating the flushing out of the microspheres.

In one embodiment of the first aspect, the housing material is selected based on at least one of a type of the downhole pipeline and a type of an oil well into which the downhole pipeline is to be run. By so doing, it is possible to increase the durability of the housing of the production logging apparatus.

In one embodiment of the first aspect, the downhole pipeline is divided into at least two intervals. In this embodiment, the first type of QDs and the second type of QDs are selected based on one of the at least two intervals where the apparatus is to be attached. By so doing, it is possible to use the first and second sets of QDs as identifiers for a certain interval of the downhole pipeline. The microspheres comprising the first and second sets of QDs and collected from the interval may be subsequently used to determine the local distribution of oil and water produced in vicinity of the interval.

In one embodiment of the first aspect, each of the housing material, the porous material, the hydrophilic material, and the oleophilic material is resistant to hydrochloric acid having a concentration of up to 24 wt. %. Thus, the production logging apparatus may be used even in the presence of hydrochloric acid which is strong enough and commonly used in the acid fracturing.

According to a second aspect, a production logging method is provided. The method starts with the step of attaching at least one production logging apparatus according to the first aspect to a downhole pipeline. The method then proceeds to the steps of running the downhole pipeline into an oil well and collecting a fluid from the downhole pipeline for a predefined time. The fluid comprises at least one of oil and water. After that, the method goes on to the step of using the collected fluid to identify an amount of microspheres of each of the first set of microspheres and the second set of microspheres which have been flushed out with the collected fluid from the porous material of the at least one production logging apparatus. Next, the method proceeds to the step of using the identified amount of microspheres to determine a quantity of at least one of the oil and the water collected from the downhole pipeline for the predefined time. By so doing, it is possible to monitor the status of oil wells (e.g., oil and water inflows) when or upon performing acid treatment and/or multistage acid fracturing in the oil wells.

In one embodiment of the second aspect, the at least one production logging apparatus is attached to the downhole pipeline by using a fastening element. In this embodiment, the fastening element is made of the same material as the housing of the at least one production logging apparatus. By so doing, it is possible to achieve high reliability of fastening the housing to the downhole pipeline.

In one embodiment of the second aspect, the at least one production logging apparatus comprises a first production logging apparatus and a second production logging apparatus, and the downhole pipeline has an external surface and an internal surface. In this embodiment, the first production logging apparatus is attached to the external surface of the downhole pipeline, and the second production logging apparatus is attached to the internal surface of the downhole pipeline in vicinity of the first production logging apparatus. By attaching the two production logging apparatuses in this manner, it possible to cause the microspheres to be flushed out with the fluid (i.e., oil and/or water) efficiently even if the level of the fluid is low inside the downhole pipeline.

In one embodiment of the second aspect, the downhole pipeline comprises at least one lateral opening. In this embodiment, the at least one production logging apparatus is attached on one side of the at least one lateral opening. By attaching the production logging apparatus(es) in this manner, it is possible to determine directions of oil and/or water flows in the oil well. For example, if the downhole pipeline is run into a vertical oil well and the production logging apparatus is attached below the lateral opening, and assuming that oil flow is being pumped but there are no microspheres in the oil flow, one can conclude that the oil flow is above the attachment point of the production logging apparatus.

In another embodiment of the second aspect, the at least one production logging apparatus comprises a first production logging apparatus and a second production logging apparatus. The first set of QDs of each of the first production logging apparatus and the second production logging apparatus has an apparatus-specific illumination spectrum. Similarly, the second set of QDs of each of the first production logging apparatus and the second production logging apparatus has an apparatus-specific illumination spectrum. In this embodiment, the first production logging apparatus is attached on one side of the at least one opening, and the second production logging apparatus is attached on another side of the at least one opening. By attaching the two production logging apparatuses in this manner, it is possible to determine the directions of the oil and/or water flows more accurately by analyzing the apparatus-specific illumination spectra of the QDs in the collected fluid.

In one embodiment of the second aspect, the identification step is performed as follows. At first, an illumination spectrum for each of the first type of QDs and second type of QDs is obtained by illuminating the collected fluid with at least one of an ultraviolet light and a laser light. Then, the obtained illumination spectra are used to identify the amount of microspheres of each of the first set of microspheres and the second set of microspheres in the collected fluid. By so doing, it is possible to accurately identify the amount of microspheres of each of the first set of microspheres and the second set of microspheres in the collected fluid.

In one embodiment of the second aspect, the oil well is a horizontal oil well. This makes the method according to the second aspect more flexible in use (i.e., it can be applied not only to standard vertical oil wells).

In one embodiment of the second aspect, the at least one production logging apparatus comprises a plurality of production logging apparatuses. In this embodiment, the downhole pipeline is divided into a plurality of intervals, and the plurality of production logging apparatuses is attached to the downhole pipeline such that each of the plurality of intervals is provided with or more production logging apparatuses of the plurality of production logging apparatuses. By so doing, it is possible to determine the status of the oil well (e.g., oil and/or water inflows) more accurately and efficiently.

In one embodiment of the second aspect, the plurality of intervals comprises a plurality of regular intervals. This may allow one to obtain a more uniform profile of oil and/or water inflows.

In one embodiment of the second aspect, the first set of QDs of each production logging apparatus of the plurality of production logging apparatuses has an apparatus-specific illumination spectrum, and the second set of QDs of each production logging apparatus of the plurality of production logging apparatuses has an apparatus-specific illumination spectrum. In this embodiment, the collected fluid is used to identify the amount of microspheres of each of the first set of microspheres and the second set of microspheres which have been flushed out with the collected fluid from the porous material of each production logging apparatus of the plurality of production logging apparatuses. Then, the identified amount of microspheres, which have been flushed out with the collected fluid from the porous material of each production logging apparatus of the plurality of production logging apparatuses, is used to determine the quantity of at least one of the oil and the water collected from each interval of the plurality of intervals of the downhole pipeline for the predefined time. By so doing, it is possible to obtain the profile of oil and/or water inflows for each of the intervals of the downhole pipeline.

In one embodiment of the second aspect, wherein the determination step is performed by using a machine-learning algorithm. The machine-learning algorithm may make the method according to the second aspect more automized to use.

Other features and advantages of the present disclosure will be apparent upon reading the following detailed description and reviewing the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is explained below with reference to the accompanying drawings in which:

FIGS. 1A and 1B schematically show different sectional views of a production logging apparatus attachable to a downhole pipeline in accordance with one exemplary embodiment;

FIG. 2 schematically shows an arrangement of two production logging apparatuses on the external surface of a downhole pipeline in accordance with a first exemplary embodiment;

FIG. 3 schematically shows an arrangement of two production logging apparatuses on the external surface of a downhole pipeline in accordance with a second exemplary embodiment;

FIG. 4 schematically shows an arrangement of three production logging apparatuses on the external surface of a downhole pipeline in accordance with a third exemplary embodiment;

FIG. 5 schematically shows an arrangement of six production logging apparatuses on the external and internal surfaces of a downhole pipeline in accordance with a fourth exemplary embodiment;

FIG. 6 shows a flowchart of a production logging method in accordance with one exemplary embodiment; and

FIG. 7 shows a block diagram of a computer system that may be used to implement at least some steps of the method shown in FIG. 6, in accordance with one exemplary embodiment.

DETAILED DESCRIPTION

Various embodiments of the present disclosure are further described in more detail with reference to the accompanying drawings. However, the present disclosure may be embodied in many other forms and should not be construed as limited to any certain structure or function discussed in the following description. In contrast, these embodiments are provided to make the description of the present disclosure detailed and complete.

According to the detailed description, it will be apparent to the ones skilled in the art that the scope of the present disclosure encompasses any embodiment thereof, which is disclosed herein, irrespective of whether this embodiment is implemented independently or in concert with any other embodiment of the present disclosure. For example, apparatus and/or method disclosed herein may be implemented in practice using any numbers of the embodiments provided herein. Furthermore, it should be understood that any embodiment of the present disclosure may be implemented using one or more of the elements presented in the appended claims.

The word “exemplary” is used herein in the meaning of “used as an illustration”. Unless otherwise stated, any embodiment described herein as “exemplary” should not be construed as preferable or having an advantage over other embodiments.

Any positioning terminology, such as “left”, “right”, “top”, “bottom”, “above”, “under”, etc., may be used herein for convenience to describe one element's or feature's relationship to one or more other elements or features in accordance with the figures. It should be apparent that the positioning terminology is intended to encompass different orientations of the structure and device disclosed herein, in addition to the orientation(s) depicted in the figures. As an example, if one imaginatively rotates the apparatus in the figures 90 degrees clockwise, elements or features described as “top” and “bottom” relative to other elements or features would then be oriented, respectively, “right” and “left” relative to the other elements or features. Therefore, the positioning terminology used herein should not be construed as any limitation of the present disclosure.

Furthermore, although the numerative terminology, such as “first”, “second”, etc., may be used herein to describe various embodiment, elements or features, these embodiments, elements or features should not be limited by this numerative terminology. This numerative terminology is used herein only to distinguish one embodiment, element or feature from another embodiment, element or feature. For example, a first set of microspheres discussed herein could be called a second set of microspheres, and vice versa, without departing from the teachings of the present disclosure.

The exemplary embodiments disclosed herein provide a technical solution that allows mitigating or even eliminating the drawbacks of the prior art which are mentioned in the description part “Background”. In particular, the technical solution disclosed herein provides continuous monitoring of the status of acid-treated oil wells using QD-based markers. In context of the present disclosure, the acid-treated oil well may refer to a vertical or horizontal oil well that has been or will be subjected to acid treatment or multistage acid fracturing. For example, the acid treatment may be used both for well workover and for stimulation of a carbonate formation. Hydrochloric acid is a commonly used acid in the acid treatment and the multistage acid fracturing. When hydrochloric acid interacts with a carbonate rock, a chemical reaction occurs, as a result of which dendrite-like fractures are formed in the carbonate rock. These dendrite-like fractures increase the area of the formation rock that can give off oil increases, thereby increasing the amount of oil produced from the oil well.

FIGS. 1A and 1B schematically show different sectional views of a production logging apparatus 100 attachable to a downhole pipeline 102 in accordance with one exemplary embodiment. More specifically, FIG. 1A shows the longitudinal section of the production logging apparatus 100, and FIG. 1B shows the cross-section of the production logging apparatus 100. The downhole pipeline 102 may be represented, for example, by a completion string or a liner.

As shown in FIGS. 1A and 1B, the production logging apparatus 100 comprises a housing 104 that is attached to the external surface of the downhole pipeline 102 by using one or more fastening elements (not shown in FIGS. 1A and 1B), such, for example, as one or more screws, clamps, clips, etc. The housing 104 and the fastening elements may be made of the same material that may be selected based on a plurality of parameters, for example, the attachment point of the housing 104 to the downhole pipeline 102, depending on whether the downhole pipeline 102 is assembled at a wellsite or factory site, and/or whether the production logging apparatus 100 is used in non-cemented well completion or cemented well completion, etc. The housing 104 preferably has a (circular) cross-section that corresponds to that of the downhole pipeline 102, which also provides its better engagement with the downhole pipeline 102. The housing 104 accommodates a porous material 106 and is provided with a plurality of holes (not shown in FIGS. 1A and 1B) through which a formation fluid may enter and exit the housing 104 when the formation fluid is pumped by using the downhole pipeline 102.

The porous material 106 may be represented by a polymer material or a sponge-like material and has QD-based markers (schematically shown as crisscrosses in FIG. 1A) embedded thereinto. It should be noted that the porous material 106 used in the production logging apparatus 100 is different from the so-called filler usually used in the existing QD-based marker technologies. Upon coming into contact with the formation fluid, the filler swells, forming gel-like structures which are diffusion channels for the QD-based markers pre-embedded into the filler. In other words, the diffusion channels serve as transport arteries for the QD-based markers, allowing them to leave the filler and be carried away by the formation fluid. Instead, the porous material 106 has such diffusion channels immediately (i.e., before its contact with the formation fluid), for which reason the formation fluid may flush out the QD-based markers from the porous material 106 more efficiently.

As for the QD-based markers (also referred to as quantum marker-reporters in the prior art), they are represented by a first set of microspheres and a second set of microspheres. Each microsphere of the first set of microspheres is made of a hydrophilic or water-attractable material and filled with a first type of QDs. Each microsphere of the second set of microspheres is made of an oleophilic or oil-attractable material and filled with a second type of QDs. It should be noted that hydrophilic microspheres may be made oleophilic by treating their surfaces with amphiphilic copolymers. The amphiphilic copolymers have hydrophilic portions by which the amphiphilic copolymers are sorbed on the surfaces of the hydrophilic microspheres, as well as hydrophobic portions by which the amphiphilic copolymers are facing outward. The microspheres are preferably filled with colloidal QDs during the synthesis of the microspheres themselves. Some non-restrictive examples of synthesis methods include the dispersion polymerization of vinyl monomers or the dispersive polycondensation of heterofunctional monomers. Each microsphere in each of the first set of microspheres and the second set of microspheres has a microsphere size that is less than the size of the holes provided in the housing 104, which also facilitates their flushing out from the housing 104 of the production logging apparatus 100. The microspheres may be about 0.2-10 microns in diameter depending on their purpose (e.g., for use inside the downhole pipeline 102 or for use between different pipelines). In one embodiment, the first type of QDs may be identical to the second type of QDs. In another embodiment, the first type of QDs and the second type of QDs may have different illumination spectra (i.e., be associated with different colors), so that it will be possible to use the first and second types of QDs as identifiers for the first and second sets of microspheres, respectively.

To make it possible to use the apparatus 100 in an acid-treated oil well, each of the material of the housing 104, the porous material 106, the hydrophilic material, and the oleophilic material should be resistant to an acid to be pumped into the oil well (i.e., should not react chemically with the acid). For this purpose, the housing 104 may be made of any alloy steel, while each of the porous material 106, the hydrophilic material, and the oleophilic material may be represented by a polymer having a polymer chain that do not contain functional groups hydrolysable in an acidic medium between the constituent repeating links of the chain (i.e., ester bonds, amide bonds, bonds specific to polyheteroarylenes). Furthermore, such a polymer should not contain terminal functional groups, especially amino groups. For example, the polymers meeting these conditions include those obtained by means of polymerization (e.g., such as polystyrene, polyolefins, chlorinated polymers), as well as those obtained by means of polycondensation (e.g., such as aminoplasts, the polycondensation of which proceeds with complete conversion of functional groups of urea, triaminotriazine and other amine-containing compounds). In one embodiment, the materials of the constructive elements of the apparatus 100 may be selected such that the apparatus 100 is resistant to hydrochloric acid having a concentration of up to 24 wt. %.

In some embodiments, the materials of the constructive elements of the apparatus 100 may be selected such that the production logging apparatus 100 (i.e., the housing 104 and the porous material 106) may be configured to release the QD-based markers for up to 5 years or longer. For this purpose, the above-described materials may be used. The production logging apparatus 100 may be also configured to release the QD-based markers continuously as long as the formation fluid flows through the production logging apparatus 100.

It should be noted that the arrangement of the apparatus 100, as shown in FIGS. 1A and 1B, is not intended to be any limitation of the present disclosure, but merely used to provide a general idea of how the apparatus 100 may be attached to the downhole pipeline 102. The apparatus 100 may be attached to the internal and/or external surface of a completion string (which is one example of the downhole pipeline 102). For example, for oil wells with cemented completion, the apparatus 100 may be preferably attached to the internal surface of the completion string or somehow arranged inside the completion string. For the oil wells with non-cemented completion, the apparatus 100 may be preferably attached to the external surface of the completion string such that it forms a cleave or sub.

In some embodiments, a plurality of production logging apparatuses 100 may be distributed (e.g., uniformly) along the downhole pipeline 102. For example, the downhole pipeline 102 may be conveniently divided into a plurality of intervals, and each of the plurality of intervals may be provided with one or more of the plurality of production logging apparatuses 100 (e.g., 1 to 6 production logging apparatuses 100 may be attached to a single interval). The intervals may either regular or irregular (e.g., when it is required to obtain the profile of water and/or oil inflows from a particular range of depths, one may arrange the production logging apparatuses 100 at these depths much more densely than at other depths). Each interval may be 50-100 meters long, and the length of each production logging apparatus 100 for one such interval may be in the range of 1.5-8 meters. In general, the selection of the length of the production logging apparatus 100 may be based on one or more criteria, such, for example, as a well production rate, a water encroachment, a gas factor, a monitoring duration, etc. In the meantime, each of the first and second sets of microspheres in each of the plurality of production logging apparatuses 100 may be provided with the apparatus-specific first and second types of QDs, respectively. In other words, the QDs used in the microspheres of each production logging apparatus 100 may be specific to an interval, i.e., provide a specific signature for the interval. Therefore, when different types of QDs are used for different intervals of the downhole pipeline 102, each type of QDs may function as an identifier for specific microspheres because different QDs have different illumination spectra when they are illuminated by lasers and/or ultraviolet light.

Let us now consider some possible arrangements of the production logging apparatuses 100 in each interval of a downhole pipeline (like the pipeline 102).

FIG. 2 schematically shows an arrangement 200 of two production logging apparatuses 100 on the external surface of a downhole pipeline 202 in accordance with a first exemplary embodiment. The downhole pipeline 202 is assumed to be run into a horizontal oil well and implemented as a completion string or liner that is divided into a plurality of regular intervals. Each regular interval has a plurality of lateral openings 204 (which may serve as inlets for the formation fluid) and is provided with the two production logging apparatuses 100. More specifically, in this embodiment, the two production logging apparatuses 100 may be arranged on both sides of the openings 204. If each of the two production logging apparatuses 100 has apparatus-specific types of QDs, as discussed above, the arrangement 200 of the two production logging apparatuses 100 may be used to determine the side or direction of the fluid flow (by analyzing the fluid samples collected from the downhole pipeline 202 for a predefine time).

FIG. 3 schematically shows an arrangement 300 of two production logging apparatuses 100 on the external surface of a downhole pipeline 302 in accordance with a second exemplary embodiment. The downhole pipeline 302 is again assumed to be run into a horizontal oil well and implemented as a completion string or liner that is divided into a plurality of regular intervals. Each regular interval has a plurality of lateral openings 304 (which may serve as inlets for the formation fluid) and is provided with the two production logging apparatuses 100. Similar to the arrangement 200, in the arrangement 300, the two production logging apparatuses 100 may be provided on both sides of the openings 304. Unlike the arrangement 200, there are blocks 306 in the arrangement 300, which act as isolation elements that may be attached to the ends of the interval. The arrangement 300 may be also used to determine from which side the formation fluid is flowing, provided that each of the two production logging apparatuses 100 has apparatus-specific types of QDs.

FIG. 4 schematically shows an arrangement 400 of three production logging apparatuses 100 on the external surface of a downhole pipeline 402 in accordance with a third exemplary embodiment. The downhole pipeline 402 is assumed to be run into a horizontal oil well and implemented as a perforated completion string or pre-perforated liner that is divided into a plurality of regular intervals. Each regular interval has a plurality of lateral openings 404 (which may serve as inlets for the formation fluid) and is provided with the three production logging apparatuses 100. As follows from the arrangement 400, the more lateral openings the downhole pipeline has, the more production logging apparatuses 100 should be arranged thereon. In other words, the more an oil and/or water inflow is, the more the QD-based markers are consumed, and, accordingly, the more such QD-based markers should be used.

FIG. 5 schematically shows an arrangement 500 of six production logging apparatuses 100 on the external and internal surfaces of a downhole pipeline 402 in accordance with a fourth exemplary embodiment. The downhole pipeline 502 is assumed to be run into a horizontal oil well and implemented in the same manner as the downhole pipeline 402. The arrangement 500 may be advantageously used when the level of a formation fluid 504 inside the downhole pipeline 502 is low, for which reason the external production logging apparatuses 100 (schematically shown as solid black boxes in FIG. 5) may not capture the formation fluid 504 efficiently. Therefore, in the arrangement 500, the external production logging apparatuses 100 are combined with the internal production logging apparatuses 100 (schematically shown as dashed black boxes in FIG. 5). The internal production logging apparatuses 100 may be arranged inside the downhole pipeline 502 in vicinity of the external production logging apparatuses 100 (e.g., under the corresponding external production logging apparatuses 100). Such a combination of the external and internal production logging apparatuses 100 may ensure that the formation fluid 504 will flow through at least some of them, thereby increasing the efficiency of the well-status monitoring in case of low fluid levels.

FIG. 6 shows a flowchart of a production logging method 600 in accordance with one exemplary embodiment. Each of the steps of the method 600 is described below in detail.

The method 600 starts with a step S602, in which one or more production logging apparatuses 100 are attached to a downhole pipeline. The downhole pipeline may be conveniently divided into a plurality of intervals, and each of the plurality of intervals may be provided with one or more production logging apparatuses 100. As discussed above with reference to FIGS. 2-5, the selection of certain arrangements of the production logging apparatuses 100 may depend on a variety of criteria, such, for example, as a fluid level inside the downhole pipeline (see the arrangement 500), tasks for which the production logging apparatuses 100 are used (e.g., the determination of a fluid flow direction—see the arrangements 200 and 300), etc. The downhole pipeline may be then run into the oil well in a step S604.

Further, in a step S606, a fluid comprising oil and/or water is collected from the downhole pipeline for a predefined time. When the fluid passes through the production logging apparatus(es) 100 (due to the holes formed in the housing(s) 104), the hydrophilic microspheres are flushed out with water and the oleophilic microspheres are flushed out with oil. More specifically, when the fluid flows through the housing 104, the mechanical energy of the fluid flow exceeds the adhesion of the microspheres to the porous material 106 inside the housing 104, thereby making the microspheres to disengage from the porous material 106 and leave the housing 104 through the holes formed therein. The collected fluid sample may thus include two portions, i.e., a water portion and an oil portion disposed above the water portion. Because oil is lighter than water, water and oil are separated in the collected fluid sample such that the hydrophilic and oleophilic microspheres are also separated in the collected fluid sample. In more detail, the hydrophilic microspheres stay in the water portion, while the oleophilic microspheres stay in the portion oil in the collected fluid sample. Therefore, the water and oil portions may be analyzed separately.

Next, the method 200 goes on to a step S608, in which the collected fluid is used to identify an amount of microspheres of each of the first set of microspheres and the second set of microspheres which have been flushed out with the collected fluid from the porous material(s) of the production logging apparatus(es). In other words, the step S608 consists in determining how many hydrophilic and oleophilic microspheres are contained in the collected fluid. The step S608 may be performed by illuminating the collected fluid sample with an ultraviolet light and/or a laser light. Then, the obtained illumination spectra are used to identify the amount of the hydrophilic and oleophilic microspheres in the collected fluid.

After that, the method 600 proceeds to a step S610, in which the identified amounts of the hydrophilic and oleophilic microspheres are used to determine quantities of the oil and/or the water collected from the downhole pipeline for the predefined time. The quantity of the water collected from the downhole pipeline is determined based on the amount of the hydrophilic microspheres contained in the collected fluid. The quantity of the oil collected from the downhole pipeline is determined based on the amount of the oleophilic microspheres contained in the collected fluid. In some embodiments, when each of the production logging apparatuses 100 has apparatus-specific QDs encapsulated in the microspheres, the amounts of the hydrophilic and oleophilic microspheres in the fluid collected from the plurality of intervals may be used to calculate the effectiveness of the intervals (i.e., the distribution of oil and water in the intervals). For this purpose, the step S610 may be performed by using a machine-learning algorithm (e.g., a pre-trained neural network). For example, assuming that the downhole pipeline is divided into 3 intervals and based on the analysis of the hydrophilic and oleophilic microspheres in the collected fluid, it may be determined that 40% of the oil is received from interval 1, 10% of the oil is received from interval 2, and 50% of the oil is received from interval 3. Similarly, it may be determined, for example, that 50% of the water is received from interval 1, 10% of the water is received from interval 2, and 40% of the water is received from interval 3.

The method 600 may be especially useful for the analysis of horizontal oil wells. The horizontal oil wells may be classified by types based on the distributions of oil and water in different intervals. The types of the horizontal oil wells may be used to estimate surroundings of the horizontal oil wells. The surrounding may include locations of the nearest injection wells. The locations of the nearest injection wells may be analyzed to provide recommendations concerning the operation of the injection wells, like filling the injection wells with polymers (to block production channels) or drilling an additional injection well nearby the horizontal well, or converting one of the production horizontal wells into the injection well.

In one alternative embodiment, the method 600 may comprise, instead of the step S602, other steps in which the hydrophilic and oleophilic microspheres are added directly to an acidic composition that is used, for example, to stimulate carbonate formations in the oil well, and the acidic composition with the added microspheres is then injected into the oil well. In this embodiment, the hydrophilic and oleophilic microspheres are fixed by their adsorption on the surface of the dendritic structure of a carbonate reservoir, which is formed by means of the chemical reaction between carbonates and the acidic composition. Further, the hydrophilic and oleophilic microspheres may be desorbed and carried away by the formation fluid flow, so that they may be further analyzed in the same manner as described above with reference to the use of the production logging apparatus(es) 100.

FIG. 7 shows a block diagram of a computer system 700 that may be used to implement at least some of the steps of the method 600 in accordance with one exemplary embodiment. The computer system 700 may be implemented as computing systems, networks, servers, or combinations thereof. The computer system 700 comprises one or more processor units 702 and a main memory 704. The main memory 704 stores, in part, instructions and data for execution by the processor unit 702. The main memory 704 stores a processor-executable code which, when executed by the processor unit 702, cause the processor units 702 to perform the steps of the method 600. The computer system 700 further comprises a mass data storage 706, a portable storage device 708, output devices 710, user input devices 712, a graphics display system 714, and peripheral devices 716. The components shown in FIG. 7 are depicted as being connected via a single bus 718. The components may be connected through one or more data transport means.

The processor unit 702 and the main memory 704 are connected via a local microprocessor bus, and the mass data storage 706, the peripheral device(s) 716, the portable storage device 708, and the graphics display system 714 are connected via one or more input/output (I/O) buses.

The mass data storage 706, which may be implemented as a magnetic disk drive, a solid-state drive, or an optical disk drive, is a non-volatile storage device for storing data and instructions for use by the processor unit 702. The mass data storage 706 stores system software for implementing embodiments of the present disclosure for purposes of loading that software into the main memory 704 as the processor-executable code.

The portable storage device 708 operates in conjunction with a portable non-volatile storage medium, such as a flash drive, floppy disk, compact disk, digital video disc, or Universal Serial Bus (USB) storage device, to input and output data and codes to and from the computer system 700. The system software for implementing embodiments of the present disclosure is stored on such a portable medium and input to the computer system 700 via the portable storage device 708.

The user input devices 712 may provide a portion of a user interface. The user input devices 712 may comprise one or more microphones, an alphanumeric keypad, such as a keyboard, for inputting alphanumeric and other information, or a pointing device, such as a mouse, a trackball, stylus, or cursor direction keys. The user input devices 712 may also comprise a touchscreen. Additionally, the computer system 700 may comprise the output devices 710. Some examples of the output devices 710 include speakers, printers, network interfaces, and monitors.

The graphics display system 714 may comprise a liquid crystal display (LCD) or other suitable display device. The graphics display system 714 may be configured to receive textual and graphical information and processes the information for output to the display.

The peripheral devices 716 may comprise any type of computer support device to add additional functionality to the computer system 700.

The components provided in the computer system 700 are those typically found in computer systems that may be suitable for use with embodiments of the present disclosure and are intended to represent a broad category of such computer components that are well-known in the art. Thus, the computer system 700 may be a personal computer (PC), handheld computer system, telephone, mobile computer system, workstation, tablet, phablet, mobile phone, server, minicomputer, mainframe computer, wearable, or any other computer system. The computer system 700 may also comprise different bus configurations, networked platforms, multi-processor platforms, and the like. Various operating systems may be used including UNIX, LINUX, WINDOWS, MAC OS, PALM OS, QNX ANDROID, IOS, CHROME, and other suitable operating systems.

At least some of the embodiments disclosed herein may be implemented in software that is cloud-based. In some embodiments, the computer system 700 is implemented as a cloud-based computing environment, such as a virtual machine operating within a computing cloud. In other embodiments, the computer system 700 itself may comprise a cloud-based computing environment, where the functionalities of the computer system 700 are executed in a distributed fashion. Thus, the computer system 700, when configured as a computing cloud, may comprise pluralities of computing devices in various forms, as will be described in greater detail below.

In general, a cloud-based computing environment is a resource that typically combines the computational power of a large grouping of processors (such as within web servers) and/or that combines the storage capacity of a large grouping of computer memories or storage devices. Systems that provide cloud-based resources may be utilized exclusively by their owners or such systems may be accessible to outside users who deploy applications within the computing infrastructure to obtain the benefit of large computational or storage resources.

The cloud may be formed, for example, by a network of web servers that comprise a plurality of computing devices, such as the computer system 700, with each server (or at least a plurality thereof) providing processor and/or storage resources. These servers may manage workloads provided by multiple users (e.g., cloud resource customers or other users). Typically, each user places workload demands upon the cloud that vary in real-time, sometimes dramatically. The nature and extent of these variations typically depends on the type of business associated with a certain user.

Although the exemplary embodiments of the present disclosure are described herein, it should be noted that any various changes and modifications could be made in the embodiments of the present disclosure, without departing from the scope of legal protection which is defined by the appended claims. In the appended claims, the word “comprising” does not exclude other elements, steps or operations, and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. 

1. A production logging apparatus attachable to a downhole pipeline, comprising: a housing made of a housing material, the housing comprising a plurality of holes each having a hole size; a porous material provided in the housing; a first set of microspheres embedded into the porous material, each microsphere of the first set of microspheres being made of a hydrophilic material and filed with a first type of quantum dots (QDs); and a second set of microspheres embedded into the porous material, each microsphere of the second set of microspheres being made of an oleophilic material and filled with a second type of QDs, wherein each microsphere in each of the first set of microspheres and the second set of microspheres has a microsphere size that is less than the hole size, and wherein each of the housing material, the porous material, the hydrophilic material, and the oleophilic material is resistant to an acid to be pumped into the oil well.
 2. The apparatus of claim 1, wherein the first type of QDs is identical to the second type of QDs.
 3. The apparatus of claim 1, wherein the first type of QDs has a first illumination spectrum and the second type of QDs has a second illumination spectrum, the second illumination spectrum being different from the first illumination spectrum.
 4. The apparatus of claim 1, wherein the microsphere size is selected based on an attachment point of the apparatus to the downhole pipeline.
 5. The apparatus of claim 4, wherein the microsphere size ranges from about 0.2 to 10 microns.
 6. The apparatus of claim 1, wherein the porous material comprises a polymer or a sponge-like material.
 7. The apparatus of claim 1, wherein the housing is made of a housing material selected based on at least one of a type of the downhole pipeline and a type of an oil well into which the downhole pipeline is to be run.
 8. The apparatus of claim 1, wherein the downhole pipeline is divided into at least two intervals, and wherein the first type of QDs and the second type of QDs are selected based on one of the at least two intervals where the apparatus is to be attached.
 9. The apparatus of claim 1, wherein each of the housing material, the porous material, the hydrophilic material, and the oleophilic material is resistant to hydrochloric acid having a concentration of up to 24 wt. %.
 10. A production logging method comprising: attaching at least one production logging apparatus according to any one of claims 1 to 9 to a downhole pipeline; running the downhole pipeline into an oil well; collecting a fluid from the downhole pipeline for a predefined time, the fluid comprising at least one of oil and water; based on the collected fluid, identifying an amount of microspheres of each of the first set of microspheres and the second set of microspheres which have been flushed out with the collected fluid from the porous material of the at least one production logging apparatus; and based on the identified amount of microspheres, determining a quantity of at least one of the oil and the water collected from the downhole pipeline for the predefined time.
 11. The method of claim 10, wherein said attaching comprises attaching the at least one production logging apparatus to the downhole pipeline by using a fastening element, the fastening element being made of the same material as the housing of the at least one production logging apparatus.
 12. The method of claim 10, wherein the at least one production logging apparatus comprises a first production logging apparatus and a second production logging apparatus, and the downhole pipeline has an external surface and an internal surface, and wherein said attaching comprises attaching the first production logging apparatus to the external surface of the downhole pipeline, and attaching the second production logging apparatus to the internal surface of the downhole pipeline in vicinity of the first production logging apparatus.
 13. The method of claim 10, wherein the downhole pipeline comprises at least one lateral opening, and wherein said attaching comprises attaching the at least one production logging apparatus on one side of the at least one lateral opening.
 14. The method of claim 13, wherein the at least one production logging apparatus comprises a first production logging apparatus and a second production logging apparatus, the first set of QDs of each of the first production logging apparatus and the second production logging apparatus has an apparatus-specific illumination spectrum, and the second set of QDs of each of the first production logging apparatus and the second production logging apparatus has an apparatus-specific illumination spectrum; and said attaching comprises attaching the first production logging apparatus on one side of the at least one opening and attaching the second production logging apparatus on another side of the at least one opening.
 15. The method of claim 10, wherein said identifying comprises: obtaining an illumination spectrum for each of the first type of QDs and second type of QDs by illuminating the collected fluid with at least one of an ultraviolet light and a laser light; and based on the obtained illumination spectra, identifying the amount of microspheres of each of the first set of microspheres and the second set of microspheres in the collected fluid.
 16. The method of claim 10, wherein the oil well is a horizontal oil well.
 17. The method of claim 10, wherein the at least one production logging apparatus comprises a plurality of production logging apparatuses, and wherein said attaching comprises: dividing the downhole pipeline into a plurality of intervals; and attaching the plurality of production logging apparatuses to the downhole pipeline such that each of the plurality of intervals is provided with one or more production logging apparatuses of the plurality of production logging apparatuses.
 18. The method of claim 17, wherein the plurality of intervals comprises a plurality of regular intervals.
 19. The method of claim 17, wherein the first set of QDs of each production logging apparatus of the plurality of production logging apparatuses has an apparatus-specific illumination spectrum, and the second set of QDs of each production logging apparatus of the plurality of production logging apparatuses has an apparatus-specific illumination spectrum; and said identifying comprises identifying, based on the collected fluid, the amount of microspheres of each of the first set of microspheres and the second set of microspheres which have been flushed out with the collected fluid from the porous material of each production logging apparatus of the plurality of production logging apparatuses; and said determining comprises determining, based on the identified amount of microspheres which have been flushed out with the collected fluid from the porous material of each production logging apparatus of the plurality of production logging apparatuses, the quantity of at least one of the oil and the water collected from each interval of the plurality of intervals of the downhole pipeline for the predefined time.
 20. The method of claim 19, wherein said determining is performed by using a machine-learning algorithm. 